1998 Feb 23
11
NXP Semiconductors
Product specification
3 W mono BTL audio amplifier with DC
volume control
TDA7056AT
TEST AND APPLICATION INFORMATION
Test conditions
T
amb
= 25
°
C if not specified: V
P
= 12 V; V
DC
= 1.4 V;
f = 1 kHz; R
L
= 16
Ω
; audio bandpass: 22 Hz to 22 kHz.
In Figures 5 and 6 a low-pass filter of 80 kHz was applied.
It should be noted that capacitive loads (100 pF and 5 nF)
connected between the output pins to a common ground
can cause oscillations. The BTL application circuit diagram
is shown in Fig.14. To avoid instabilities and too high
distortion, the input and power ground traces must be
separated as far as possible and connected together as
close as possible to the IC. The quiescent current has
been measured without load impedance.
Voltage gain
The maximum closed-loop voltage gain has been
internally fixed at 35.5 dB. The input sensitivity at
maximum gain for P
o
= 3 W (R
L
= 16
Ω
) is 115 mV.
The gain bandwidth is 20 Hz to 300 kHz within 1 dB.
Output power
The output power as a function of supply voltage has been
measured at THD = 10%. The maximum output power is
limited by the maximum allowed power dissipation at
T
amb
= 25
°
C approximately 2 W, and the maximum
available output current is 1.25 A repetitive peak current.
Switch-on/switch-off
The switch-on behaviour depends on the following:
•
The rise time of the power supply (if t
r
> 40 ms for
V
P
= 0 to 12 V then the switch-on behaviour will be
good)
•
The input capacitor and source impedance (a higher
source impedance and/or lower input capacitor value
will have a positive influence on the switch-on/switch-off
behaviour)
•
The DC volume control pin (a capacitor of >0.1
μ
F
avoids disturbances).
Thermal behaviour:
The measured thermal resistance of the IC package is
highly dependent on the configuration and size of the
application board. Data may not be comparable between
different semiconductors manufacturers because the
application boards and test methods are not (yet)
standardized. The thermal performance of packages for a
specific application may also be different than presented
here, because the configuration of the application boards
(copper area) may be different. NXP Semiconductors uses
FR-4 type application boards with 1 oz copper traces with
solder coating. The measurements have been carried out
with vertical placed boards.
Using a practical PCB layout with wider copper tracks and
some copper area to the IC pins and just under the IC, the
thermal resistance from junction to ambient can be
reduced. In the demonstration application PCB the
R
th(j-a)
= 56 K/W for the SO20 plastic package. For a
maximum ambient temperature of T
amb
= 50
°
C the
following calculation can be made for the maximum power
dissipation:
For the application at V
P
= 12 V and R
L
= 16
Ω
the worst
case sine wave dissipation is 1.85 W. Because in practice
the ‘music-power’ causes about the half of the sine wave
dissipation, this application (V
P
= 12 V; R
L
= 16
Ω
) has
been allowed.
Short-circuit protection:
The output pins (pins 14 and 17) can be short-circuited to
ground respectively to +V
P
. The Missing Current Limiter
(MCL) protection circuit will shut-off the amplifier.
Removing the short-circuit will reset the amplifier
automatically. Short-circuit across the load
(pins 14 and 17) will activate the thermal protection circuit;
this will result in reducing the short-circuit current.
150 K/W
50 K/W
–
(
)
56 K/W
-----------------------------------------------------
1.79 W
=
